1. Field of the Invention
The present invention relates to ionic liquids and a method of preparing the same, and more particularly, to ionic liquids and a method of preparing the same, whereby the ionic liquids are partially or completely miscible with various polar and/or non-polar solvents, and can be used as a phase transfer catalyst at room temperature, thereby reducing manufacturing costs. Examples of the polar or non-polar solvent may include water, or various organic solvents such as alcohols, acids, olefins, paraffins, aromatics, aliphatics, amines, ethers, esters, ketones, aldehydes, amides, nitriles, and nitroalkanes.
2. Description of the Related Art
In general, ionic liquids are defined as molten salts with melting point below 100° C. Due to their relatively low melting point, ionic liquids can be used as solvent or co-solvent where chemical reaction may be carried out. The applications of ionic liquids are rapidly growing in various technical fields because their chemical and physical characteristics can be readily modulated by tailoring the natures of cation and anion.
According to U.S. Pat. Nos. 5,827,602, 5,731,101, and 7,208,605, certain types of ionic liquids can be used in the applications of non-aqueous batteries, electrochemical capacitors, electroplating, catalysis and chemical separations. Since ionic liquids solely consist of a pair of ions (cation and anion) rather than molecules, it has shown very special distinctiveness, such as high reactivity and specific selectivity, in comparison with ordinary organic solvent.
Solvent properties, such as melting/boiling points, viscosity, solubility, or polarity, always influence the overall performance of chemical reactions as well as other applications. In this aspect, a great number of efforts have been made to tailor those properties of ionic liquids for desirable properties. U.S. Pat. No. 5,731,101 discloses low temperature ionic liquids that contain metal halides. (A. P. Abbott, J. C. Barron, K. S. Ryder, D. Wilson, Chem.-Eur. J. 13, 6495 (2007)). Lowering melting points through this way resulted from eutectic effect between metal halide and quaternary ammonium salts. Despite the melting temperature lowering effect, the polarity controls are quite limited in this case because of the presence of metal and halide ions.
Tuning the hydrophobic/hydrophilic balance is another important issue in the aspect of reaction engineering. There are two conventional ways to adjust the hydrophobicity in common ionic liquids. The hydrophobicity of ionic liquid can be raised by increasing alkyl chins in a cation site of ionic liquid. Alternatively, anion substitution can give further adjustment of the hydrophobicity. For example, ionic liquids having an anion, such as BF4−, PF6−, or (CF3SO2)2N−, frequently exhibit strong hydrophobicity, which are not readily miscible with water. However, these approaches often cause increases of melting points and viscosity of the ionic liquids as well.
In recent years, ionic liquids have been paid much attention for substitutes of common organic solvent. To satisfy the desirable solvent, they much have a wide range of solubility as well as stability in diverse environments. Most ionic liquids have selective miscibility in either polar or non-polar compounds at room temperature. Ionic liquids with versatile solubility in both polar and non-polar solvent are rarely reported up to now.
The use of ionic liquid containing alkyl sulfate anion as phase transfer catalysts is discussed in U.S. Pat. No 7,252,791. In particular the miscibility with non-polar solvent normally depends on the alkyl group, which is located at either organic cation or sulfate anion. In industrial aspects, those ionic liquids have less economically viable due to the high cost of alkyl sulfate anions.
Taking into account above listed solvent properties, it would be desirable to have ionic liquids with versatile miscibility in a wide range of solvent for chemical reaction, electrochemical applications, and heat and/or charge transfer media. Furthermore, it would be more advantageous to produce the ionic liquids using relatively low cost materials compared to those of the prior art.